An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharp focused image can be obtained? Find the size and nature of the image.
Here, Object distance, u = -27 cm (To the left side of mirror)
Image distance, v = ? (To be calculated)
Focal length, f = -18 cm (It is a concave mirror)
Height of object, h1 = 7.0 cm
And, Height of image, h2 = ? (To be calculated)
Now, For a mirror: 
Image distance, v = -54 cm
Since the image distance is minus 54 cm, therefore, the screen should be placed at a distance of 54 cm in front of the concave mirror (on its left side). The nature of image obtained on the screen is real and inverted.
Also, For a mirror, 
= -14.0 cm
Thus, the size of image is 14.0 cm.